1. Field of the Invention
This disclosure relates to a negative active material for a rechargeable lithium battery, and a rechargeable lithium battery including the same.
2. Description of the Related Art
In recent times, due to reductions in size and weight of portable electronic equipment, there has been a need to develop batteries for use in the portable electronic equipment where the batteries have both high performance and large capacity. Batteries generate electric power by using materials capable of electrochemical reactions at positive and negative electrodes.
For example, a rechargeable lithium battery generates electricity due to change of chemical potentials when lithium ions are intercalated/deintercalated at positive and negative electrodes. The rechargeable lithium battery includes a material that can reversibly intercalate/deintercalate lithium ions as positive and negative active materials, and also an organic electrolyte or a polymer electrolyte.
As for negative active materials for a rechargeable lithium battery, various carbon-based materials such as artificial graphite, natural graphite, and hard carbon have been used because the carbon-based materials have good cycle-life characteristics and safety characteristics.
In order to provide a high-capacity rechargeable battery, there have been efforts to improve utility of a carbon-based active material and charge density per electrode volume. Recently, the rechargeable lithium battery using a carbon-based material as a negative active material exhibiting a capacity corresponding to a theoretical capacity (372 mAh/g) of graphite have been developed. Furthermore, charge density improvement also reaches a limit.
Therefore it is difficult to additionally improve the capacity of a battery using currently available carbon-based materials. In order to provide a high capacity rechargeable lithium battery, a metal material including silicon (Si), tin (Sn), or the like having a higher charge and discharge capacity compared to graphite has drawn attention as a negative active material for a rechargeable lithium battery, which is disclosed in Japanese Patent No. 2997741 and U.S. Pat. No. 5,395,711 to Tahara et al.
However, the volume of the metal-based material is too easily changed during charging and discharging, so, in the rechargeable lithium battery including the same, the negative active material layer is easily collapsed and the physical and electrical bond can not be maintained in the negative electrode. What is therefore needed is an improved negative active material for a rechargeable lithium battery that improves capacity but does not expand and contract upon charging and discharging.